锁相环电压-频率-窄脉冲转换特性的改善及应用

介绍锁相环 (PLL)电压 -频率 -窄脉冲转换原理及其微功耗机制 ,并结合集成锁相环路特性及其随环境温度的变化 ,提出了优化锁相环线性度的方案和改善频率 -温度特性的温度补偿电路。该电路已应用于光纤光推动高压电流传感器的测量探头中 ,其功耗小于 0 .3mW。     

AutoCAD在机构综合中的应用

利用计算机辅助设计中的图形处理技术,实现常用机构的图解法综合。作图求解精度可达到解析法的求解精度。用于解决机械原理多媒体辅助教学软件中有关机构综合问题,取得了明显的效果。     

基于神经网络的弹性连杆机构振动主动控制

研究基于神经网络的弹性连杆机构振动主动控制方法.介绍了双隐层动态递归神经 网络的数学模型,利用实验数据离线设计了神经网络辨识器与神经网络控制器.采用基于神 经网络的间接自适应控制策略对弹性连杆机构实施了振动主动控制,机构的动力学品质得到 显著改善.实验结果证明了该方法的有效性.     

电荷泵中电流失配的讨论

电荷泵锁相环在电子通讯技术中的应用非常广泛,本文分析了电荷泵的工作原理以及它对锁相环性能的影响,讨论了电荷泵中的电流失配现象,给出了从晶体管尺寸和电路结构两方面减小电流失配的方法。     

浅论计算机病毒及检测方法

本文从病毒的定义、计算机病毒自身特征、病毒分类、病毒发展的特点、计算机病毒的基本机制、计算机病毒的检测方法几个方面来说明计算机系统是脆弱的,计算机病毒的危害是巨大的。因此,为了确保信息的安全与畅通,一定要作好对病毒的检测防范工作。     

Design of distributed compliant micromechanisms with an implicit free boundary representation

In this paper, a parameterization approach is presented for structural shape and topology optimization of compliant mechanisms using a moving boundary representation. A level set model is developed to implicitly describe the structural boundary by embedding into a scalar function of higher dimension as zero level set. The compactly supported radial basis function of favorable smoothness and accuracy is used to interpolate the level set function. Thus, the temporal and spatial initial value problem is now converted into a time-separable parameterization problem. Accordingly, the more difficult shape and topology optimization of the Hamilton–Jacobi equation is then transferred into a relatively easy size optimization with the expansion coefficients as design variables. The design boundary is therefore advanced by applying the optimality criteria method to iteratively evaluate the size optimization so as to update the level set function in accordance with expansion coefficients of the interpolation. The optimization problem of the compliant mechanism is established by including both the mechanical efficiency as the objective function and the prescribed material usage as the constraint. The design sensitivity analysis is performed by utilizing the shape derivative. It is noted that the present method is not only capable of simultaneously addressing shape fidelity and topology changes with a smooth structural boundary but also able to avoid some of the unfavorable numerical issues such as the Courant–Friedrich–Levy condition, the velocity extension algorithm, and the reinitialization procedure in the conventional level set method. In particular, the present method can generate new holes inside the material domain, which makes the final design less insensitive to the initial guess. The compliant inverter is applied to demonstrate the availability of the present method in the framework of the implicit free boundary representation.     

Gas-phase ion chemistry in organometallic systems

This review essentially deals with positive ion/molecule reactions occurring in gas-phase organometallic systems, and encompasses a period of time of approximately 7 years, going from 1997 to early 2004. Following the example of the excellent review by Eller & Schwarz (1991; Chem Rev 91:1121-1177), in the first part, results of reaction of naked ions are presented by grouping them according to the neutral substrate, while in the second part, ligated ions are grouped according to the different ligands. Whenever possible, comparison among similar studies is attempted, and general trends of reactivities are evidenced.     

甘肃景电灌区次生盐化土壤的性质及其发生机理

本文对甘肃景电灌区次生盐化土壤的理化性质进行了研究 .该区次生盐渍化土壤主要为硫酸盐氯化物和氯化物硫酸盐型 ,水溶性钠离子在阳离子中占绝对优势 .土壤通体碳酸钙含量很高 ,并有少量的石膏 .钠离子饱和度很高 ,具有钠质特性或钠质化现象 ,盐化与钠质化同时进行 .在此基础上对次生盐渍化的机理和改良进行了讨论     

一种基于地理位置的无线传感器网络安全路由协议

提出了一种基于地理位置的无线传感器网络安全路由协议。该协议将安全因素引入路由选择机制,将能量、距离以及安全三个因素作为优选路径的标准;利用基于六边形部署信息的密钥预分布方案来分配节点间的通信密钥,建立完善的数据传输机制,保证了数据的机密性、完整性和新鲜性;通过采用辅助机制,增强了协议抵御网络攻击的能力。仿真结果和性能分析表明,该协议在抵御网络攻击方面具有良好的性能,与已有协议相比,在提高能源利用的有效性,及延长网络生命周期方面有较优的表现。